1. Field of the Invention
This invention relates to an oil well sucker rod safety block. More specifically, the invention relates to a safety knock-off block that during operation completely encircles the sucker rod and will not open up or slip off the well head.
2. Description of the Prior Art
The basic concept of providing a device commonly called a knock-off block when servicing or repairing oil field pumping equipment is a well established practice. The so-called knock-off block is a spacer used to support the string of sucker rods in the oil well while work is being done on the engine or motor, gear box, pump jack, bridle or any other part of the aboveground pumping equipment. Ordinarily, the knock-off block is made from a two inch pipe or the like that has an approximately one and a half inch wide slot cut longitudinally along the length of the pipe. The slotted pipe than has two horseshoe shaped steel plates welded to the top and bottom with the open sides in alignment with the slot in the pipe. To use the knock-off block, the pump jack is stopped at the top of the stroke. The slot in the knock-off block is placed over the polish rod and the knock-off block is held in place by hand or is fastened in place, usually using wire or rope as the fastener. The pump jack is then lowered so that the polish rod liner head engages the knock-off block. The pump jack is lowered to the bottom of the stroke and stopped. Work can then be performed on the pump equipment.
This type of knock-off block is well known for its dangerous behavior. It sometimes slips off the polish rod after weight is applied by lowering the rods, thus breaking the fastening devices and risking personal injury.
Various attempts have been made to alleviate the above problem with limited commerical success. For example, in U.S. Pat. No. 1,196,647 spring biased jaws that surround the polish rod are provided to prevent the polish rod from exiting the slot. Such a solution is not fail-safe in that the device can still malfunction or be opened during use. Thus, a need for an inexpensive yet reliable safety block that cannot be removed or accidentally opened during use still exists.